1. Field of the Invention
The present invention relates to an imaging apparatus and its control method, and particularly relates to auto focus (hereinafter abbreviated as “AF”) control based on a photoelectric conversion signal output from an imaging element.
2. Description of the Related Art
One focus detection method performed by an imaging apparatus is an imaging plane phase-difference type method that detects a focus state using focus detecting pixels formed in an imaging element. Another focus detection method performed by an imaging apparatus is a contrast type method that detects a focus state using a contrast evaluation value based on a shot imaging signal output from an imaging element.
Japanese Patent Laid-Open No. 2013-25246 discloses an imaging plane phase-difference type imaging apparatus that includes a contrast evaluating unit and a correlation calculating unit and compares two absolute values of focus evaluation ranges obtained from these units to thereby determine the focus evaluation value of an object by the comparison result. The contrast evaluating unit determines a contrast focus position based on the contrast evaluation value of a signal obtained by shift summation of imaging signals from different pupil areas. Thus, a focus position can be specified without actually driving a focus lens for AF control.
However, Japanese Patent Laid-Open No. 2013-25246 does not disclose any concrete solution against a low-brightness object which is disadvantageous for the contrast evaluating unit as compared with the correlation calculating unit and the result evaluation under a saturation condition. Thus, it may become difficult to perform shooting in an in-focus state if focus detection cannot be performed by the contrast evaluating unit.